1. Field of the Invention
The present invention relates to an organic electroluminescence device (hereinafter also referred to as “device” or “organic EL device”). In particular, the invention relates to an organic electroluminescence device with excellent durability at a high brightness.
2. Description of the Related Art
In recent years, organic electroluminescence devices (organic EL devices) are being actively researched and developed because light emission with high brightness is obtained by low-voltage driving. In general, organic EL devices are configured of organic layers including a light emitting layer and a pair of electrodes interposing the foregoing layers therebetween and are one in which an electron injected from a cathode and a hole injected from an anode recombine with each other in the light emitting layer, and energy of a formed exciton is utilized.
In recent years, high efficiency of the device is being advanced by using a phosphorescent material. Iridium complexes, platinum complexes and so on are known as the phosphorescent light emitting material (see, for example, JP-A-2005-220136).
There is known a technique for enhancing the luminous efficiency and durability of an organic EL device by using a platinum complex having a tetradentate ligand (see, for example, WO 04/108857). Among such platinum complexes, complexes having a pyridylpyridine structure are able to shorten the emission wavelength relative to complexes having a phenylpyridine structure and are promising as a light-blue to blue light emitting material. However, there has not been reported a light emitting material with excellent durability.
Also, there are known a light emitting material having a pyridylpyridine structure and an organic EL device using the same (see JP-A-2006-261623). JP-A-2006-261623 discloses that an organic EL device having high emission brightness, high luminous efficiency and high durability is obtained.